What a difference a year makes. Last autumn the Arsenal manager, Arsène Wenger, was generally seen bent double on the touchline, his agony at his team’s decline evident in his every Basil Fawlty contortion.

Twelve months on and he is smiling again, his humour restored, his sarcasm towards the media resharpened (“You really should be a coach,” he mocked one quizzical reporter at Upton Park).

And the odd thing is, if a year ago we had known that he would be facing this season shorn of the ambitious Robin van Persie, the man without whom his side would surely have finally driven him into a straitjacket, a smile would have been the last thing we expected to see on his face.

But here he was leaving east London twinkling, thrilled not only with the result, not only with the manner of his team’s comeback against a stubborn West Ham, but with the fact that the goals were shared among his forwards.

Even his new recruit Olivier Giroud scored a smart goal, the sort of instinctive finish that seemed beyond him when he first arrived from France.

What was making him smile even more, however, was further evidence that he may well have pulled off the transfer coup of his career. Latterly, Arsenal have been developing a reputation as a selling club, their function chiefly to provide personnel for the Mancunian juggernauts. But this summer, Wenger demonstrated his purchasing prowess by bringing from Malaga Santi Cazorla.

Once again here he was the man who made the difference, his dipping, swerving shot from the edge of the area finally deflating a perky, determined home side.

And that goal – worth his inclusion on its own – was by no means his only contribution. He buzzed around the pitch, providing his team-mates with a constant flow of clever passes. His disguised ball allowing Giroud a late chance which he was unable to convert is without question the most delicious delivery of the season.

“He makes everybody a better player,” said Wenger of the Spaniard. And he has a point. With the quick-witted Lukas Podolski abetting him in the visitors’ midfield, he was simply too sharp, too subtle, too elusive for a home side whose industry could not be faulted.

Watching Kevin Nolan panting in his wash, what makes him so slippery is the fact he is so comfortable using either foot. Asked afterwards whether the player favours his right or his left, Wenger confessed he had no idea.

“When you watch him play, you don’t know what foot he is,” the manager reckoned.

It may seem odd that in a profession which involves the feet, but this is a rare quality in football. Wenger himself could only think of two players similarly astute with either boot: Glenn Hoddle and John Terry. Cazorla, however, does not simply bamboozle with his ambidextrousness.

He applies it to the collective cause. Playing just ahead of Aaron Ramsey and Mikel Arteta – whose instruction before the game was clearly “win the ball and give it to Santi” – he had so much possession the Opta computers must have required additional memory.

Not that, to start with, he had it all his way. West Ham began well, absolutely playing to their strengths. Andy Carroll in particular was soon punching aggressive holes into the always porous Arsenal backline.

Every time a ball was lofted forward into the visitors’ half, it seemed to land on his forehead.

Actually, it seemed to land on his forehead when it was swung into the home half too, his defensive contribution so significant if Roy Hodgson were looking for a ready replacement for John Terry and Rio Ferdinand, he could do worse than employ the muscular ponytail at the back for England.

So diverted were the Arsenal ­centre-backs by the striker on loan from Liverpool’s presence, they barely noticed Mohamed Diame stealing past Ramsey into an inviting space to open the scoring.

A year ago, this might have been the signal for Arsenal to crumble. Wenger was forever banging on about his side’s character back then, even when it appeared they shared the constitution of a jellyfish.

But here they really did respond, with a lovely finish from Theo Walcott sandwiched between Giroud and Cazorla’s efforts. Now, they really do look a team that really has belief that it can overcome adversity. Now they have Cazorla.

“It is too early to say what effect he will have on us,” said Wenger, apparently applying his wilful vision to the most compelling evidence of the new man’s influence.

“But when you consider that this type of player is not even playing in Spain, it shows you how good they [the Spanish] are.”